Adamantane based three-dimensional rigid-rod polymers

ABSTRACT

High compressive strength, three-dimensional para-oriented benzobisoxazole polymers of the formula:  represents repeating units of the formula:   &lt;IMAGE&gt;

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured and used by or forthe Government of the U.S. for all governmental purposes without thepayment of any royalty.

BACKGROUND OF THE INVENTION

This invention relates to three-dimensional, rigid-rod polymers havingbenzobisazole polymer chains attached to an adamantane core.

The low compressive strengths of para-oriented benzobisoxazole polymerfilms and fibers have restricted their use in certain high-performanceapplications despite their excellent tensile properties, chemicalresistance and thermooxidative stability.

We have prepared a three-dimensional para-oriented benzobisoxazolepolymer having greater compressive strength than the one-dimensionalpolymers.

Accordingly, it is an object of the present invention to provide athree-dimensional para-oriented benzobisoxazole polymer.

It is another object of this invention to provide a method for preparinga three-dimensional para-oriented benzobisoxazole polymer.

Other objects and advantages of the present invention will be apparentto those skilled in the art.

SUMMARY OF THE INVENTION

In accordance with the present invention there are providedthree-dimensional para-oriented benzobisoxazole polymers of the formula:##STR4## wherein Q is ##STR5## and wherein Z represents repeating unitsof the formula: ##STR6##

The adamantane-based three-dimensional rigid-rod polymers of thisinvention are prepared by the polycondensation of an AB-type monomer,such as 4-(5-amino-6-hydroxybenzoxazole-2-yl)benzoic acid (ABA) with atetracarboxy-substituted adamantane, such as1,3,5,7-tetrakis(4-carboxylatophenyl) adamantane (TCPA) or1,3,5,7-adamantanetetracarboxylic acid (ATC), in polyphosphoric acid(PPA). The stoichiometry of the AB-type monomer to thetetracarboxy-substituted adamantane (molar ratio) used in thepolycondensation reaction determines the length of thepoly(benzo(1,2-d:4,5-d')bis-oxazole-2,6-diyl)-1,4-phenylene (PBO)chains. In general, the quantity of the tetracarboxy-substitutedadamantane relative to the AB-type monomer can range from about 0.1 to5.0 mol %.

Briefly, the polymerization process comprises the following steps: (i)solution of the AB-type monomer and the tetracarboxy-substitutedadamantane monomer in 77% polyphosphoric acid (PPA) at a temperature ofroom temperature up to about 50°-65° C.; (ii) addition of P₂ O₅ to raisethe P₂ O₅ content of the medium to 83%; (iii) chain propagation andcyclodehydration; and (iv) precipitation of the polymer into water,followed by washing the polymer with ammonium hydroxide and with hotwater and drying the polymer in vacuum at 110° C.

Solution step (i) is generally carried out for about 1-24 hours. Chainpropagation and cyclodehydration step (iii) is generally carried out a atemperature of about 120° to 190° C. for about 20-50 hours.

The polymers of this invention can be cast into film or fiber at thetime of precipitation (step iv, above); alternatively, they can beprecipitated, washed and dried as discussed previously, then dissolvedin a strong acid, such as methanesulfonic acid (MSA), then spin-castinto fibers or cast into film.

The polymers of the present invention are also useful as reinforcingcomponents in molecular composites. Such composites are disclosed, forexample, in Helminiak et al, U.S. Pat. No. 4,207,407, issued Jun. 10,1980. These composites comprise a flexible, coil-like aromaticheterocyclic matrix polymer and a para-oriented benzobisazole polymer.In these composites, the ratio, by weight, of matrix polymer torigid-rod polymer can range from about 95:5 to about 1:1. Suchcomposites may be employed as monolithic structures for a variety ofapplications, but particularly in high temperature environments.

The following examples illustrate the invention:

EXAMPLE I Preparation of Model Compound

Stoichiometric quantities of 2-aminophenol and1,3,5,7-tetrakis(4-carboxylatophenyl)adamantane (TCPA)were reacted inpolyphosphoric acid at 190° C. A nearly quantitative yield of thedesired model compound,1,3,5,7-tetrakis(4-2-benzoxazolyl)phenyl)adamantane, was obtained. Thestructure of the model compound was verified by infrared and massspectroscopy.

EXAMPLE II Preparation of Three-Dimensional Polymer I

A slurry solution of 6.55 g of 77 percent polyphosphoric acid, 3.54 g ofphosphorus pentoxide, 1.89 g (7 mmol) of4-(5-amino-6-hydroxybenzoxazole-2-yl)benzoic acid (ABA) and 0.043 g(0.07 mmol) of 1,3,5,7-tetrakis(4-carboxylatophenyl)adamantane (TCPA)was stirred under a stream of dry nitrogen for two hours at roomtemperature. The temperature was then slowly increased to 100° C. over aperiod of two hours. After stirring for 20 hours at this temperature,stir opalescence was observed in the viscous colution. The reactiontemperature was raised to 120° C. for 5 hours, 150° C. for one hour, andthen to 165° C. for 24 hours. The reaction mixture exhibited an intense,but not persistent stir opalescence and became so extremely viscous thatstirring had very little effect. The reaction temperature was finallyraised to 190° C. After 10 hours, the reaction mixture was poured intowater and the precipitated polymer was vigorously stirred in a blenderwith water. The resulting fibrous polymer was stirred in 5 percent NH₄OH for 4 hours and in distilled water for 2 hours. After being extractedwith water for 24 hours and methanol for 4 hours in a continuousextraction apparatus, the polymer was dried at 100° C. in vacuo for twodays. 1.61 g of golden-yellow polymer was obtained (96% yield). Thepolymer had an intrinsic viscosity of 13.5 gl/g in methanesulfonic acidat 30° C. The IR spectrum of the the polymer exhibited absorptions at1579, 1558, 1498, 1411, 1362, 1115, 1053, 1009, 853, 819 and 753 cm⁻¹.Elemental analysis: Calculated for C₁₄₂₀ H₆₂₂ N₁₉₈ O₁₉₈ : C, 72.20; H,2.65; N, 11.74. Found: C, 70.72; H, 2.68; N, 11.64.

The golden-yellow polymer was soluble only in methanesulfonic acid orpolyphosphoric acid. The polymer structure was verified by elementalanalysis and comparison of the polymer IR spectrum with the modelcompound spectrum. The spectra were consistent with the proposedstructures and did not exhibit absorptions indicative of unreactedcarboxylic acid, amine or hydroxy moieties. No evidence of carbonylfunctional groups attributable to uncyclized amide or ester groups wasobserved.

EXAMPLE III

A series of polymerizations was conducted at polymer concentrations of10 and 14%, and TCPA concentrations of 0, 1 and 2 mol %, as shown in thefollowing table:

                  TABLE I                                                         ______________________________________                                        Trial                                                                              ABA,    TCPA,   Polymer conc.,                                                                          Stir    Intrinsic                              No.  mol %   mol %   % (w/w)   opalescent                                                                            viscosity                              ______________________________________                                        I-1  100     0       10        Yes     13.3                                   I-2  99      1       10        Yes     12.5                                   I-3  100     0       14        Yes     16.8                                   I-4  99      1       14        Yes     13.5                                   I-5  98      2       14        Yes     9.6                                    ______________________________________                                         Intrinsic viscosities (dl/g) were measured in methanesulfonic acid at         30° C.                                                            

Examination of the data in the Table reveals that incorporation of the1,3,5,7-tetra substituted adamantane core component led to lower polymerintrinsic viscosities than achieved by homopolymerization reactions ofABA. Polymer concentrations of 10 and 14 percent (w/w) (Trials No. 2 and4) at one percent TCPA molar content led to three-dimensional rigid-rodpolymers with intrinsic viscosities of 12.5 and 13.5 dl/g, respectively,as compared to intrinsic viscosities of 13.3 and 16.8 dl/g for theanalogous homopolymerization reaction (Trials No. 1 and 3). Underidentical reaction conditions at 14 percent (w/w) polymer concentration,an even lower intrinsic viscosity (9.6 dl/g) was observed with a twopercent TCPA molar content (Trial No. 5)

The thermooxidative stability of the three-dimensional rigid-rodpolymers is very high, as shown by thermogravimetric analysis (TGA) inair and isothermogravimetric analysis (ITGA) at 260° C. in circulatingair. The onset of weight loss under TGA did not occur until thetemperature reached 500° C. Under ITGA, a weight loss of six percent wasobserved after 216 hours. Thermogravimetric/mass analysis (TG/MS) invacuo indicated that the three-dimensional rigid-rod polymer is quitesimilar to one-dimensional PBO concerning the primary degradationproducts: CO, HCN, H₂ O, CO₂, NH₃, CH₄, C₆ H₅ CN, and C₆ H₆. A smallamount of CO₂ was released at relatively low temperatures before theevolution of the bulk of the CO₂ product, perhaps an indication ofdegradation of carboxylic acid end groups. Differential scanningcalorimetry gave no eviddence of a glass transition temperature.

The polymer obtained in Trial No. 5 was spun from PPA solution intofiber. The mechanical properties of this fiber are compared toone-dimensional PBO fiber in the following table:

                  TABLE II                                                        ______________________________________                                                                 Tensile                                                         Compressive   Strength Modulus                                     Polymer    Strength (Ksi)                                                                              (Ksi)    (Msi)                                       ______________________________________                                        1-dimensional                                                                            32            330      13                                          3-dimensional                                                                            43            134      11.3                                        ______________________________________                                    

EXAMPLE IV Preparation of Three-Dimensional Polymer II

A series of polymerizations was conducted at a polymer concentration of14%, using the monomers 4-(5-amino-6-hydroxybenzoxazole-2-yl)benzoicacid (ABA) and 1,3,5,7-adamantanetetracarboxylic acid (ATC) in a mannersimilar to that described in Example II, above, as shown in thefollowing table:

                  TABLE III                                                       ______________________________________                                        Trial                                                                              ABA,    ATC,    Polymer conc.,                                                                          Stir    Intrinsic                              No.  mol %   mol %   % (w/w)   opalescent                                                                            viscosity                              ______________________________________                                        II-1 99      1       14        Yes     11.5                                   II-2 98      2       14        Yes     6.9                                    II-3 97      3       14        Yes     7.2                                    II-4 95      5       14        Yes     6.7                                    ______________________________________                                         Intrinsic viscosities (dl/g) were measured in methanesulfonic acid at         30° C.                                                            

Elemental analysis for polymer II-2: Calculated for C₁₃₉₂ H₆₁₂ N₁₉₆ O₁₉₆: C, 72.01; H, 2.66; N, 11.85. Found: C, 70.05; H, 2.63; N, 11.69.

Various modifications may be made in the instant invention withoutdeparting from the spirit and scope of the appended claims.

We claim:
 1. A three-dimensional para-oriented benzobisazole polymer ofthe formula: ##STR7## wherein Q is ##STR8## wherein Z representsrepeating units of the formula: ##STR9##
 2. The polymer of claim 1wherein the quantity of the adamantane core unit is about 0.1 to 5.0 mol% of said polymer.
 3. A three-dimensional para-oriented benzobisazolepolymer of the formula: ##STR10## wherein Q is

    --Z--COOH

wherein Z represents repeating units of the formula: ##STR11##
 4. Thepolymer of claim 3 wherein the quantity of the adamantane core unit isabout 0.1 to 5.0 mol % of said polymer.